David Pleasure

Sensory neuropathy from pyridoxine abuse. A new megavitamin syndrome

We describe seven adults who had ataxia and severe sensory-nervous-system dysfunction after daily high-level pyridoxine (vitamin B6) consumption. Four were severely disabled; all improved after withdrawal. Weakness was not a feature of this condition, and the central nervous system was clinically spared. Although consumption of large doses of pyridoxine has gained wide public acceptance, this report indicates that it can cause sensory neuropathy or neuronopathy syndromes and that safe guidelines should be established for the use of this widely abused vitamin.

Arthrogryposis: a review and update.

Congenital contractures can be divided into two groups: isolated contractures and multiple contractures (Fig. 1). Isolated congenital contractures affect only a single area of the body; the most common isolated contracture is congenital clubfoot, which occurs in one of every 500 live births1. Fig. 1 Types of congenital contractures. The term arthrogryposis is often used as shorthand to describe multiple congenital contractures that affect two or more different areas of the body. Arthrogryposis is not a specific diagnosis, but rather a clinical finding, and it is a characteristic of more than 300 different disorders2,3. The overall prevalence of arthrogryposis is one in 3000 live births4. The inheritance, natural history, treatment guidelines, and outcomes of arthrogryposis vary among disorders, underscoring the importance of making a specific diagnosis in each child1,5-10. The purpose of this article is to present the current state of knowledge about the classification, etiology, and management of children with various types of arthrogryposis. To establish a differential diagnosis, it is important to first decide whether a child has normal neurological function. A normal neurological examination suggests that arthrogryposis is due to amyoplasia, a distal arthrogryposis, a generalized connective tissue disorder, or fetal crowding. In contrast, an abnormal neurological examination indicates that movement in utero was diminished as a result of an abnormality of the central or peripheral nervous system, the motor end plate, or muscle. ### Amyoplasia Amyoplasia (A = no; myo = muscle; plasia = growth) is a distinct form of arthrogryposis with characteristic clinical features as shown in Figure 2: the shoulders are usually internally rotated and adducted, the elbows are extended, the wrists are flexed and ulnarly deviated, the fingers are stiff, and the thumbs are positioned in the palm. In the lower limbs, …

Prospects for Minocycline Neuroprotection

Minocycline is a clinically available antibiotic and anti-inflammatory drug that also demonstrates neuroprotective properties in a variety of experimental models of neurological diseases. There have thus far been more than 300 publications on minocycline neuroprotection, including a growing number of human studies. Our objective is to critically review the biological basis and translational potential of this action of minocycline on the nervous system.

Glutathione turnover in cultured astrocytes: Studies with [15N]glutamate

Abstract: The incorporation of [15N]glutamic acid into glutathione was studied in primary cultures of astrocytes. Turnover of the intracellular glutathione pool was rapid, attaining a steady state value of 30.0 atom% excess in 180 min. The intracellular glutathione concentration was high (20–40 nmol/mg protein) and the tripeptide was released rapidly into the incubation medium. Although labeling of glutathione (atom% excess) with [15N]glutamate occurred rapidly, little accumulation of 15N in glutathione was noted during the incubation compared with 15N in aspartate, glutamine, and alanine. Glutathione turnover was stimulated by incubating the astrocytes with diethylmaleate, an electrophile that caused a partial depletion of the glutathione pool(s). Diethylmaleate treatment also was associated with significant reductions of intraastrocytic glutamate, glycine, and cysteine, i.e., the constituents of glutathione. Glutathione synthesis could be stimulated by supplementing the steady‐state incubation medium with 0.05 mM L‐cysteine, such treatment again partially depleting intraastrocytic glutamate and causing significant reductions of 15N labeling of both alanine and glutamine, suggesting that glutamate had been diverted from the synthesis of these amino acids and toward the formation of glutathione. The current study underscores both the intensity of glutathione turnover in astrocytes and the relationship of this turnover to the metabolism of glutamate and other amino acids.

Antibodies to oligodendroglia in patients with multiple sclerosis

We demonstrated antibodies to isolated oligodendrocytes and to oligodendroglia in brain sections by indirect immunofluorescence technic in serums of 19 of 21 patients with multiple sclerosis. We also found such antibodies in three of five patients with subacute sclerosing panencephalitis and one of four patients with acute disseminated encephalomyelitis, but not in patients with other neurologic diseases or normal persons. The antibodies were absorbed by preincubation of serum with isolated oligodendrocytes or whole white matter, but not with purified myelin or liver tissue. Immunofluorescent staining was blocked by either rabbit anti-oligodendrocyte serum or non-fluoresceinated goat anti-human immunoglobulin. These findings suggest that antibodies to oligodendroglia are distinct from antibodies to myelin and that demyelination in multiple sclerosis could be a consequence of an immunopathologic reaction directed against oligodendroglial cells.

PATHOPHYSIOLOGY OF OLIGODENDROGLIAL EXCITOTOXICITY

Oligodendrocyte‐like cells (OLD) derived from the rat oligodendroglial precursor line, CG‐4, express Ca2+‐permeable non‐methyl‐D‐aspartate glutamate receptor channels (GluR). Exposure to kainate, an L‐glutamate analogue, markedly elevates OLC Ca2+ influx and cytosolic [Ca2+], and results in damage to both OLC plasma membrane and OLC nuclear DNA. Two observations indicate that kainate‐induced OLC internucleosomal DNA nicking is not simply a delayed consequence of cell necrosis: 1) there is no temporal lag between onset of plasma membrane injury and of DNA nicking; and 2) aurintricarboxylic acid, an endonuclease inhibitor, blocks kainate‐induced damage to the plasma membrane. N‐acetyl‐L‐cysteine also inhibits OLC kainate injury, suggesting that reactive oxygen species participate in OLC excitotoxicity. Kainate‐induced OLC Ca2+ influx and excitotoxicity are blocked by α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionate (AMPA), indicating that these kainate effects are mediated by AMPA‐GluR. AMPA and L‐glutamate fail to elicit OLC damage unless cyclothiazide, an AMPA‐GluR desensitization blocker, is present. OLC express both the “flip” and “flop” forms of GluR2, GluR3, and GluR4 mRNAs, but neither flip nor flop GluR1 mRNA. These data, together with the restriction of the desensitization‐blocking activity of cyclothiazide to GluR containing flip‐encoded GluR subunits, and the sharply diminished Ca2+ permeability of GluR containing edited GluR2, suggest OLC excitotoxicity is mediated by AMPA‐GluR that contain flip GluR3 and/or flip GluR4 protein subunits, but neither flip nor flop GluR2 protein subunits. Rapid desensitization of these GluR is likely to be important in protecting cells of the oligodendroglial lineage from excitotoxicity.

α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors mediate excitotoxicity in the oligodendroglial lineage

Abstract: We demonstrate by reverse transcriptase‐polymerase chain reaction and Southern blotting that an immortalized rat oligodendroglial cell line (CG‐4) expresses the non‐N‐methyl‐d‐aspartate (non‐NMDA) glutamate receptor (GluR) genes GluR2–7, KA‐1, and KA‐2 and that nonimmortalized cells of the rat oligodendroglial lineage express the GluR1–3, GluR5–7, KA‐1, and KA‐2 genes. Lactic dehydrogenase release assays show that both immortalized and nonimmortalized cells of the oligodendroglial lineage are damaged by a 24‐h exposure to 500 µM kainate or 5 mMl‐glutamate, but not by a 24‐h exposure to up to 10 mMα‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionate (AMPA). Damage is prevented by the non‐NMDA GluR channel inhibitor 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione and is also averted if Ca2+ is removed from the culture medium. Cyclothiazide, which blocks desensitization of AMPA‐preferring GluRs, increases cytotoxicity of kainate as well as inducing toxicity of AMPA. We conclude that cells of the oligodendroglial lineage express a population of AMPA‐preferring and possibly also kainate‐preferring GluR channels that are capable of mediating Ca2+‐dependent excitotoxicity and that AMPA‐induced cytotoxicity is blocked by desensitization of AMPA‐preferring GluRs.

Pyramidal Neurons Are Generated from Oligodendroglial Progenitor Cells in Adult Piriform Cortex

Previous studies have shown that oligodendroglial progenitor cells (OPCs) can give rise to neurons in vitro and in perinatal cerebral cortex in vivo. We now report that OPCs in adult murine piriform cortex express low levels of doublecortin, a marker for migratory and immature neurons. Additionally, these OPCs express Sox2, a neural stem cell marker, and Pax6, a transcription factor characteristic of progenitors for cortical glutamatergic neurons. Genetic fate-mapping by means of an inducible Cre–LoxP recombination system proved that these OPCs differentiate into pyramidal glutamatergic neurons in piriform cortex. Several lines of evidence indicated that these newly formed neurons became functionally integrated into the cortical neuronal network. Our data suggest that NG2+/PDGFRα+ proteolipid protein promoter-expressing progenitors generate pyramidal glutamatergic neurons within normal adult piriform cortex.

Stage-specific effects of bone morphogenetic proteins on the oligodendrocyte lineage.

Oligodendrocyte maturation is regulated by multiple secreted factors present in the brain during critical stages of development. Whereas most of these factors promote oligodendrocyte proliferation and survival, members of the bone morphogenetic protein family (BMPs) recently have been shown to inhibit oligodendrocyte differentiation in vitro. Oligodendrocyte precursors treated with BMPs differentiate to the astrocyte lineage. Given that cells at various stages of the oligodendrocyte lineage have distinct responses to growth factors, we hypothesized that the response to BMP would be stage-specific. Using highly purified, stage-specific cultures, we found that BMP has distinct effects on cultured oligodendrocyte preprogenitors, precursors, and mature oligodendrocytes. Oligodendrocyte preprogenitors (PSA-NCAM+, A2B5-) treated with BMP2 or BMP4 developed a novel astrocyte phenotype characterized by a morphological change and expression of glial fibrillary acidic protein (GFAP) but little glutamine synthetase expression and no labeling with A2B5 antibody. In contrast, treating oligodendrocyte precursors with BMPs resulted in the accumulation of cells with the traditional type 2 astrocyte phenotype (GFAP+, A2B5+). However, many of the cells with an astrocytic morphology did not express GFAP or glutamine synthetase unless thyroid hormone was present in the medium. The addition of fibroblast growth factor along with BMP to either oligodendrocyte preprogenitor or the oligodendrocyte precursor cells inhibited the switch to the astrocyte lineage, whereas platelet-derived growth factor addition had no effect. Treatment of mature oligodendrocytes with BMP elicited no change in morphology or expression of GFAP. These data suggest that as cells progress through the oligodendrocyte lineage, they show developmentally restricted responses to the BMPs.

Cerebral white matter contains PDGF-responsive precursors to O2A cells

Cells dissociated from the cerebral white matter of immature rats were maintained in monolayer culture. Treatment with platelet-derived growth factor (PDGF) caused a large increase in the numbers of “O2A” oligodendroglial precursor cells (which bind the monoclonal antibody A2B5) and subsequently in the numbers of galactocerebroside (galC)- positive oligodendroglia. A2B5-negative “pre-O2A cells” in cerebral white matter cultures in which O2A cells and oligodendroglia had been killed by antibody-dependent complement-mediated cytolysis were induced by PDGF to proliferate and to differentiate into O2A cells and subsequently into oligodendroglia and type 2 astroglia. The most mature pre-O2A phenotype in these cultures was a small, round, process-bearing cell which expressed vimentin but not glial fibrillary acidic protein or galC. Cells of this phenotype were not observed upon PDGF treatment of immature rat optic nerve monolayer cultures from which O2A cells and oligodendrocytes had been depleted, and PDGF also failed to elicit the accumulation of O2A cells and oligodendroglia in such cultures.